x86: undo_limit_pages() must reset page count

... before calling __free_pages() as it is already being called in the
context of that or similar function (which used put_page_test_zero()
first or otherwise assumes the page count is zero).

Reported-by: Daniel Kiper <dkiper@xxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/arch/i386/mm/hypervisor.c
+++ b/arch/i386/mm/hypervisor.c
@@ -437,6 +437,7 @@ static void undo_limit_pages(struct page
 	BUG_ON(order > max_contig_order);
 	xen_limit_pages_to_max_mfn(pages, order, 0);
 	ClearPageForeign(pages);
+	init_page_count(pages);
 	__free_pages(pages, order);
 }